Tobacco smoke filter



Jan. 28, 1964 A. c. TANQUARY TOBACCO SMOKE FILTER Filed May 24. 1961 cfaywpfrf men/@PER POL YPYR/POL /DO/VE ,4L 515er BY United States Patent O 3,ii9,396 TBACC@ SMLKE FHJ'ER Albert C. Tanquary, White Bear Lake, Minn., assigner to Minnesota Mining and Manufacturing Company, St. Pani, Minn., a corporation of Delaware Filed May 24, i961, Ser. No. 112,203 4 Claims. (Ci. LS1- 10) This invention relates to filters for aerosols and particularly to improved filters for tobacco products, e.g., cigarettes, and comprised of polypyrrolidone fibers.

Numerous patents have been granted on filtering means for tobacco smoke. Removal has often been effected by entrainment in simple wads or plugs of fibers of cellulose or cellulose acetate alone or combined with other substances having absorptive powers. Various mechanical arrangements have been proposed which provide labyrinthne passageways or effect impingement of the smoke against a baffle to trap the aerosol particles. In general, however, simple wadding or plugs of crimped fibers appear to provide the best balance between effectiveness and cost of construction. Such wads are built up from filaments or paper strips with usually sufficient crimping to provide a labyrinth of passageways such that substantial amounts of tars and other undesirable components of the smoke are trapped therein and removed. In order that the pressure drop be not excessive, requiring an effort in smoking, the wad or plug must not be too compact and yet it must not be too loose or the filtering efficiency will be lost. It appears that in present commercial practice a wad or plug of the cross-sectional area of a cigarette with a length of about 7s inch and weighing about 1A gram meets the optimum requirements as to pressure drop, efiiciency of tar removal and economy of fabrication. Such a filter decreases the amounts of nicotine and tars carried by the smoke but still passes quite substantial amounts of both.

Other criteria in the design of filters for cigarettes are that the material should not be excessively sensitive to moisture and should remain firm to the lips of the smoker, should produce no peculiar taste and should not ignite when the burning tobacco is close. Retention of some moisture is advantageous since this tends to cool the smoke, but this should not be so extensive as to make the filter soggy or to desiccate the smoke entirely which might tend to make the smoke especially irritating.

This invention has for one object to provide a more efficient tobacco smoke filter. Another object is to provide a filter adapted to inclusion in a cigarette and which is of high efiiciency in removing tars, resins and nicotine from tobacco smoke. A further object is to provide a cigarette filter having moisture retentive properties. Still further objects will become apparent from the disclosure hereinafter.

In its broadest aspect the present invention contemplates the incorporation of fibers of polypyrrolidone in filter media. This broad invention is particularly illustrated by its embodiment in cigarette filters. When polypyrrolidine fibers are formed into cigarette filters, it has been found that a relatively high percentage of tars, nicotine, etc. are removed from the cigarette smoke.

The invention is further illustrated by the drawings herewith wherein:

FIGURE l is a perspective view of a cigarette incorporating a filter of the invention, portions being broken away to show the fibers of the filter and the tobacco.

FIGURE 2 is a perspective view of a filter of the invention wherein the polypyrrolidone fibers are longitudinally arranged in a bundle.

FIGURE 3 is a perspective view of a filter of the invention wherein the bundle consists of substantially longitudinally aligned crimped polypyrrolidone fibers.

FIGURE 4 is a perspective view of a filter of the invention wherein the polypyrrolidone fibers are in a cylindrically wadded random mat.

It is known that filaments may be made from polypyrrolidone and it is found that filaments of about l to about 10 denier are preferred for the filter media of the invention. In general, filaments of fibers of polypyrrolidone consist of polymer having molecular weights such that the inherent viscosity (at concentrations about 0.2 g. per decaliter in meta cresol) is from about 0.5 to 1.0 or higher. Since the preparation of the polymer and the filaments do not form a part of this invention and methods therefor are known in the art, these procedures will not be described further. For the purposes of this invention the particular procedures employed are immaterial.

The number of filaments or fibers required to make a satisfactory filter plug of the invention will depend on the thickness of the individual fibers and the amount of crimps they are given. It is not essential that the fibers be of the same dimensions and even fibers containing slubs can be used thus providing a means of consuming otherwise waste material. It is, however, preferred to employ fairly uniform fibers when a tow is to be laid up from contiguous fibers and for this purpose from about 2,000 to 200,000 filaments are required when the individual fibers are from l to l0 denier. The number of fibers is preferably reduced as the tow is given greater crimp. That is to say that if it is intended to give a high crimp to the fibers after making up the tow, the tow is made up to contain fewer fibers. The denier of the final tow is to be in the range of about 20,000 to 200,000 so that it is possible to estimate the effect of the crimp on the number of fibers required.

The cylindrical filter may also be made from yarns or roving containing staple fiber of lengths from about one inch upward which may include material of uneven dirnensions, as noted hereinabove, or of varying lengths including minor amounts of lengths shorter than one inch. In this case either a roving or cylindrical bundle of the desired denier may be made directly, or several smaller yarns may be plied together to produce the desired denier. Another method for producing filter elements of the invention is to prepare a mat of polypyrrolidone filters in random fashion loosely associated to permit the passage of smoke. The mat is cut into strips of suitable width and crinkled into a tow having the denier desired for the filter elements. Alternatively, the mat of randomly associated fibers can be wadded into generally cylindrical shape and confined within a paper tube, or the like. Similarly, a loosely woven fabric can be used for preparation of filter elements.

lf desired, minor amounts of pulverulent or granular absorbents such as charcoal, flour, dextrin, silica gel, and the like, may be incorporated in the tow replacing approximately equal weights of polypyrrolidone fibers so that the final denier of the tow is substantially unaltered. The reduction in the amount of fibers in this instance is necessary to prevent forming filter elements which are so compact as to impede the passage of smoke to an unwanted extent.

When the tow is assembled it is desirably crimped by any of the standard procedures, particularly if comprised of long filaments. Several individually crimped yarns may be twisted together to produce the tow or staple of crimped fibers may be used. It is particularly desirable to employ crimping in production of filter elements since it provides labyrinthine passageways for the smoke and assists in removal of aerosol particles. Crimping may be carried out to almost any commonly producible degree. A common average is from 6 to 12 crimps per inch but may be up to 50 or more crimps per inch. Much less than 6 crirnps per inch is hardly effective enough to warrant the operation.

Alternatively, the fibers can be lofted, twisted, coiled, or the like, as, for example, in the so-called Ban-lon process. Various methods aredescribedv in the report of D. F. Arthur, I. Textile Institute, v. 49, Proceedings, pp. 638-649, 1958. In this way the bulk of the fibers is increased to provide suitable labyrinthine passages. This, like crimping, prevents channeling of the smoke, which would lead to greatly lowered efficiency.

The preferred embodiments of the filter of the invention` are those in which the configuration of the bers is such as to prevent channeling after fabrication into filters. For this'purpose, crimped, lofted, twisted, coiled, or otherwise bulked polypyrrolidone fibers can be used requiring only that they have configurations equivalent to about six crimps per inch or more.

The filtering medium per se consists of a mass of substantially longitudinally aligned crimped fibers, small spaces between the fibers and groups of fibers allowing passage of the smoke therethrough. Such longitudinal alignment is particularly evident when tow or staple roving or yarn, especially that having relatively long fiber length, are used. When a random mat of fiber is used, as described hereinabove, the fibers are more randomly oriented.

A particularly useful type of crimping apparatus is the so-called stuffing-box type which readily permits adjustment of crimps or convolutions from 6 to 50 per inch or more as desired with amplitudes, that is, heights, of the convolutions of from about 0.2 inch to 0.01 inch.

The crimped tow is then compressed to cylindrical shape and encircled to the diameter of a cigarette with a suitable wrapping which may be paper or other sheet material suitable for' such purposes. Thus, it should be firm and usually substantially impermeable to air, at least not porous or foraminous. Alternatively, the exterior of the cylinder may be fused to hold the remainder of the fibers in place. The resulting article is conveniently termed a filter-tube stock. This is cut into lengths of predetermined length, e.g., A; inch, suitable for cigarette lters, to provide filter elements.

The cigarette blanks, that is, tubes of cigarette paper enclosing tobacco of the desired properties, are joined end to end with the filter elements, for example, employing circumferential seals of thin sheets of' cork or glazed water repellent paper for this purpose. Both the operation of Wrapping and combining with the cigarette blank may be carried out using existing filter-making cigarette-making machinery.

Tests of cigarette filter elements of the invention show an enhanced efhciency over commercial cigarette filters in removal of nicotine and tar with no increase in burning time of the tobacco caused by an increase in resistance to flow. Because polypyrrolidone is a polyamide-type polymer, there is a common belief that polypyrrolidone resembles the nylons. However, it is quite surprising to find that comparable cigarette filters comprising polyhexamethylene adipamide (nylon 66) are definitely inferior to filter elements of the invention with respect to removal of nicotine and tars. The dark-colored tars and resins are absorbed throughout the fibers of polypyrrolidone. In nylon or other non-absorptive fibers these materials are held substantially on the surface, with relatively little penetration of the fiber, as shown by inspection of crosssections of the fibers after use of the filters, with a microscope. These results and the superiority of the invention are more clearly shown by the following example.

Fibers of polypyrrolidone (inherent viscosity of about 1) are laid up into a tow of about 38,000 filaments each being 2.4 denier and the tow is crimped to an average of about crimps per inch, using the stufiing box method. (Elongation of a one-inch length of crimped fiber is about 1.3 inches.) Portions of the tow are hand wrapped in a manual cigarette rolling machine with standard cigarette 4 paper to give a cylinder enclosed in paper, which is cut into S; inch long filter elements weighing about 0.25 grams each.

For comparison, similar filter elements weighing about 0.23 gram each are prepared from commercial nylon 66 staple fiber crimped to 20 crimps per inch of 2.9 denier laid up into a cylinder of about 45,000 fibers.

A quantity or" commercial filter-tip cigarettes are procured and the filter tips (average weight 0.24 gram prepared from cellulose acetate fibers) are removed from twenty of them and replaced by the filter elements of the invention and the nylon 66 filter elements to give ten cigarettes with each type of filter element. These and ten of the commercially available filter-tip cigarettes are smoked in a machine so that the smoke after passing the filters passes through a glass wool trap and then through a trap containing N/ 10 sulfuric acid. The average smoking time is about 7.9 minutes per cigarette. These two traps collect substantially all of the tars, resins and nicotine which passV through the filters. After all of the cigarettes of each group are smoked the gain in weight in the first trap is recorded and chloroform is added to prevent evaporation of nicotine. The contents of the glass wool trap and the dilute sulfuric acid trap are analyzed for nicotine by ultraviolet spectral analysis. The results foundv are summarized in the following table in which the weights determined are given in milligrams:

It is evident that the filter elements of the invention comprising polypyrrolidone are markedly better than those commercially available using cellulose acetate or those produced using nylon 66 fibers.

What is claimed is:

l. In a smoking article having a wrapper enclosing tobacco, a filter within said wrapper at one end of said article consisting essentially of a smoke-permeable mass of fibers of polypyrrolidone.

2. In a smoking article having a wrapper enclosing tobacco, a filter within said wrapper at one end of said article according to claim l wherein the smoke-permeable mass of -fbers consists essentially of a bundle of polypyrrolidone fibers adapted to passage of tobacco smoke therethrough without channeling.

3. In a smoking article having a wrapper enclosing tobacco, a filter within said wrapper at one end of said article according to claim l wherein the smoke-permeable mass of fibers consists essentially of a bundle of substantially longitudinally aligned crimped polypyrrolidone fibers.

4. In a smoking article having a wrapper enclosing tobacco, a filter within said wrapper at one end of said article according to claim l wherein the smoke permeable mass of fibers consists essentially of a cylindrically wedded random mat of polypyrrolidone fibers.

References Cited in the file of this patent UNITED STATES PATENTS 2,688,380. MacHenry Sept. 7, 1954 2,707,959 Shelanske May 10, 1955 2,780,228 Touey Feb. 5, 1957 2,867,219 Hug Jan. 6, 1959 2,916,038 Wade Dec. 8, 1959 2,980,641 Cox Apr. 18, 1961 FOREIGN PATENTS 719,439 Great Britain Dec. 1, 1954 UNTTED STATES PATENT GFFICE CERTIFICATE 0F CCRRECTCN Patent No., 3g1l9396 January 287 1964 Albert Co Tanquary erted that error appears n the above numbered pat- It s hereby c t the said Letters Patent should read as erftJ requiring correetion and the, corrected belowe Column 2Q line 43V for lters' read M fibers l Signed and sealed this 22nd day of September 194 (SEAL) Attest:

EDWARD J BRENNER Commissioner of `Patents ERNEST W. SWDER ttesting fficer 

1. IN A SMOKING ARTICLE HAVING A WRAPPER ENCLOSING TOBACCO, A FILTER WITHIN SAID WRAPPER AT ONE END OF SAID ARTICLE CONSISTING ESSSENTIALLY OF A SMOKE-PERMEABLE MASS OF FIBERS OF POLYPYRROILIDONE. 